1. Field of the Invention
The present invention relates to an organic light emitting diode display, and a display panel and driving method thereof.
2. Discussion of the Related Art
Generally, organic light emitting diode (OLED) displays are display devices that emit light by electrically exciting an organic compound. An organic light emitting diode display includes N×M organic light emitting cells (or pixels) arranged in the form of a matrix, and displays an image by driving the organic light emitting cells, using voltage or current.
An organic light emitting cell has a structure including an anode electrode layer (e.g., indium tin oxide: ITO), an organic thin film, and a cathode electrode layer. To achieve an improved balance between electrons and holes, and thus an enhancement in light emitting efficiency, the organic thin film has a multi-layer structure including an emitting layer (EML), an electron transport layer (ETL), and a hole transport layer (HTL). The organic thin film also includes an electron injecting layer (EIL) and a hole injecting layer (HIL).
Methods for driving an organic light emitting diode display include a passive matrix method and an active matrix method which uses thin film transistors (TFT) to drive organic light emitting cells of the organic light emitting diode display. In the passive matrix method, an anode and a cathode are formed crossing each other, and a line is selected in order to drive an organic light emitting cell. However, in the active matrix method, a thin film transistor is coupled to an indium tin oxide (ITO) pixel electrode of an organic light emitting cell, and the organic light emitting cell operates according to a voltage maintained by the capacitance of a capacitor coupled to a gate of the thin film transistor. The active matrix method can be further divided into a voltage programming method and a current programming method according to a signal, which is applied to program a voltage of the capacitor.
In a conventional organic light emitting diode display, a pixel includes a plurality of sub-pixels having respective colors in order to express various colors, and a color is expressed by a combination of the respective colors emitted from the sub-pixels. Generally, one pixel includes a sub-pixel for red (R), a sub-pixel for green (G), and a sub-pixel for blue (B), and a color is expressed by a combination of the red, green, and blue.
However, in order to drive the sub-pixels, the respective sub-pixels must include a driving circuit for driving an organic light emitting element (e.g., an OLED), a data line for transmitting a data signal, a scan line for transmitting a scan signal, and a power line for transmitting a power voltage. Accordingly, the organic light emitting diode display must include a large number of lines (e.g., scan and data lines) and circuits for driving the pixels. The lines are difficult to arrange in the limited display area of the conventional organic light emitting display, and an aperture ratio corresponding to an emitting pixel area of the conventional organic light emitting display can be reduced.